The present invention relates to field devices of the type used in industrial processes. More specifically, the present invention relates to a field device for use in monitoring or controlling an industrial process having a removable power source.
Field devices are used in industrial processes to control or monitor operation of the process. Wireless field devices can measure any of a number of process characteristics such as, for example, pressure, level, flow velocity, mass flow, pH, temperature, density, and conductivity or can monitor process equipment for such things as vibration, strain or corrosion or can monitor the general plant environment for such things as fire and gas detection or can be used for locating the present position of workers and equipment. For example, a process variable transmitter is a type of field device which can be used to monitor a process variable of a process fluid. Examples process variables include temperature, pressure, level, flow rate, etc. A controller is a type of field device which is used to control operation of the process. For example, the controller can control a flow rate of a process fluid by adjusting a position of a valve in a pipe carrying the fluid.
Traditionally, field devices have been connected to a central control room through electrical wiring. One type of connection uses two electrical wires and is known as a two wire process signal loop. In such a configuration, the same two wires are used for communication and to power the field device. More recently, wireless communication techniques have been developed. In such a configuration, wires are not required to connect the field device to another location. One example protocol is the wireless IEC 62591 International Standard (Wireless HART®).
Some types of wireless field devices include an internal power source such that they are capable of operating without any external electrical connections. Such field devices include a power source such as a battery which is used to power the field device. Energy harvesting techniques, such as solar power supply, thermal electric generator, vibration harvester, etc., can be used to provide additional power to the device. One example of a field device which includes multiple power sources is shown in U.S. Pat. No. 7,812,480 entitled APPARATUS AND METHOD FOR ON-LINE POWER SOURCE REPLACEMENT IN WIRELESS TRANSMITTERS AND OTHER DEVICE filed Mar. 19, 2008 by Datta et al.